The most recent clinical studies have confirmed H. pylori to be the causative agent for most cases of chronic gastritis and ulcers. In addition, there is evidence that supports the association of H. pylori with gastric carcinoma. High titer serum IgG antibody responses (and less frequently IgA responses) develop in persons colonized with H. pylori. Serologic analysis may be more sensitive than diagnostic methods involving biopsies in detecting colonization. With successful antibiotic therapy, antibodies decline to negative levels in 3-6 months. When serology is "equivocal" or when low levels of antibody are detected, confirmation by Western blot may be useful.